1. Field of the Invention
This invention relates to syringe systems that are used for storing and dispensing materials therefrom, and more particularly to a hand-operated dental syringe that is capable of efficiently storing a solid, yet pliable material, such as a dental composite material or a light activating composite which cures with exposure to an activating light, and extruding precise amounts of the composition from the dental syringe.
2. Prior State of the Art
Various types of syringes have heretofore been used in dental applications, including for storing and dispensing highly viscous or solid, yet pliable dental composites. For example, standard push-type syringes comprising a barrel and a plunger may be used for such purposes. However, especially with solid, yet pliable dental compositions, it is often difficult to generate the pressure needed to express the material through the outlet opening by exerting pressure on the syringe plunger in a longitudinal direction. Another serious problem is that once sufficient pressure is applied to the plunger, it is difficult to precisely control the amount of material expelled through the outlet opening of the barrel, thereby resulting in waste of the excess material.
To overcome some of these problems, syringes having a threaded barrel and a threaded plunger have been used to extrude dental compositions. An example of such a syringe is illustrated in FIG. 1. The syringe 110 comprises a barrel 112 and a plunger 114. Barrel 112 has a central bore 116, an inlet end 118, an outlet end 120, and a threaded insert 122 located at the inlet end 118. The plunger 114 has a proximal end 124, a distal end 126, a threaded stem 128, and a T-shaped head 130. The threads of threaded stem 128 are complementary of, and configured to mate with, the threaded insert 122 of the barrel 112. By inserting the distal end 126 of plunger 114 into threaded insert 122 of barrel 112 and rotating plunger 114 relative to barrel 112 in a clockwise direction, the distal end 126 of plunger 114 is progressively advanced into the central bore 116 of barrel 112. Threaded insert 122 and threaded stem 128 cooperate to translate external rotational forces applied to T-shaped head 130 into longitudinal forces applied through the distal end 126 of plunger 114 to the material contained within the central bore 116 of barrel 112. It will be appreciated by those skilled in the art that the use of the threaded barrel and threaded plunger combination makes it easier for the user to generate the forces needed within barrel 112 to extrude the material out of the outlet end of barrel 112.
However, the threaded syringes found in the prior art have some significant disadvantages. First, such syringes require specially designed and fabricated syringe barrels, which are more difficult and more expensive to manufacture than standard, unthreaded push-type syringe barrels. In addition, such threaded syringe barrels can only be used with threaded plungers and are not, without modification, compatible or interchangeable with standard push-type plungers.
An even more serious disadvantage of the threaded syringes found in the prior art is that they do not provide any means for relieving the pressure built up within the barrel when the external forces are removed from the syringe plunger. As shown in FIG. 1, the prior art syringes typically include relatively fine threads, which result in a relatively high coefficient of friction between the threaded insert 122 of barrel 112 and the threaded stem 128 of plunger 114. Those skilled in the art will appreciate that significant pressures can be generated within barrel 112 as plunger 114 is advanced into barrel 112 by rotating plunger 114 relative to barrel 112, particularly when solid, yet pliable dental compositions are situated within barrel 112. Once the external rotational forces are removed from plunger 114, the fine pitch of the threads coupled with the friction between threaded insert 122 and threaded stem 128 prevent the pressure built up within barrel 112 from forcing plunger 114 to back out from within barrel 112. Instead, the pressure built up within barrel 112 continues to force the dental composition to flow through the outlet end 120 of barrel 112, even after the external forces have been removed from plunger 114, thereby resulting in waste of the excess material.
Yet another disadvantage associated with the threaded syringes found in the prior art is that the fine threads used in such devices collect debris and other contaminants which, in turn, make it more difficult to sterilize and maintain the sterile condition of the device.